1. Field of the Invention
The present invention relates to an integrated service digital network (ISDN) terminal adapter connectable between a terminal and an ISDN, and more particularly, to an ISDN terminal adapter where both data communication by packet switching and data communication by circuit switching can be established.
2. Description of the Related Art
In an ISDN terminal adapter where both data communication by packet switching and data communication by circuit switching can be established, either data communication by packet switching or data communication by circuit switching is selected automatically or manually.
In the prior art, an automatic changing operation is carried out in accordance with the amount of data to be transmitted (see JP-A-HEI3-175855), a call facility (see JP-A-HEI3-159444), a combination of data to be transmitted, a transmission distance and a kind of communication (see JP-A-HEI3-101452), a charge calculated based upon amount of data (JP-A-HEI3-45053), or registered dialing information (JP-A-HEI3-40633).
In the above-mentioned prior art, however, even if a fault is generated in data communication by packet switching, it is impossible to automatically change from data communication by packet switching to data communication by circuit switching. Also, even if a large amount of delay is generated in the transmission of data communication by packet switching, it is impossible to automatically change from data communication by packet switching to data communication by circuit switching. Further, it is impossible to monitor the of transmission speed of data communication by packet switching.